The present invention relates a method for removing a guanidine compound from aqueous media. More particularly, it relates a method for removing an ionic or a neutral, or both an ionic and a neutral guanidine compound from aqueous media.
Guanidine compounds are frequently used as catalysts in chemical reactions, for example because of their basic properties in the case of neutral guanidine compounds or because of their phase transfer catalytic properties in the case of ionic guanidine compounds (also know as guanidinium salts). In particular examples U.S. Pat. No. 5,229,482 discloses a displacement method for the preparation of polyetherimides from bis(chlorophthalimides) and alkali metal salts of dihydroxy-substituted aromatic hydrocarbons using a solvent of low polarity such as o-dichlorobenzene in the presence of a thermally stable phase transfer catalyst such as a hexaalkylguanidinium halide. U.S. Pat. No. 5,830,974 discloses a similar method using a monoalkoxybenzene such as anisole as solvent. Isolation of product from organic media comprising a guanidine compound often involves washing the organic media with water. In these cases all or at least a portion of guanidine compound may transfer to the aqueous phase. For proper disposal of the wash water and for recovery and reuse of valuable guanidine compounds, a method is needed to remove a guanidine compound from the aqueous media.
U.S. Pat. No. 5,759,406 teaches removal of adsorbates such as guanidinium salts from brine solution using a non-ion-exchangeable adsorbent polymeric resin. However, the polymeric resins show limited adsorption capacity and must be used in relatively large amounts for efficient removal of the target adsorbates.
U.S. Pat. No. 6,214,235 teaches purification of brine solution for electrolysis by removal of organic salts using carbonaceous adsorbents. However, the method requires brine solutions with concentration of salt greater than 5 weight percent and makes no suggestion for recovery of organic salts. There is a continuing need for a method to remove guanidine compounds from aqueous media, particularly for wastewater treatment and disposal, and for recovery of guanidine compounds for further use.